1. Field of the Invention
The present invention relates to a method of analyzing oxygen or nitrogen contained in a titanium group metal or an alloy thereof. More particularly, it is concerned with a method of quantitatively determining oxygen contained in such metal or alloy by melting the metal or alloy at a high temperature in an inert gas atmosphere to react the oxygen with carbon, extracting it as carbon monoxide and analyzing the latter. It is also concerned with a method of quantitatively determining nitrogen contained in such metal or alloy by melting the metal or alloy at a high temperature in an inert gas atmosphere to thereby extract the nitrogen and analyzing it.
2. Description of the Prior Art
It is well known that oxygen contained as a valuable element in for example titanium, like nitrogen contained therein, is occluded between the crystal lattices of titanium and exerts a great influence on strength and other mechanical properties. And the content of such oxygen or nitrogen is specified also in the Material Standards. Therefore, advancement of the technique for adjusting and controlling the content of oxygen or nitrogen contained in titanium is desired, and at the same time, also as to the technique for analyzing such oxygen or nitrogen, it is necessary to make a thorough study.
Heretofore, as the method of analyzing oxygen contained in titanium, there has generally been adopted a method in which a sample for analysis (hereinafter referred to simply as "sample") is placed in a crucible made of graphite, then heat-melted at a high temperature in an inert gas atmosphere such as helium to allow reaction to proceed as shown by the following formula (1) and the resulting carbon monoxide is extracted and then determined quantitatively according to an infrared absorption method or a thermal conductivity method. EQU C+O=CO(g) (1)
For analysis of nitrogen contained in titanium, there has generally been adopted a method in which a sample is placed in a graphite crucible, then heat-melted at a high temperature in an inert gas atmosphere such as helium to allow reaction to take place as shown by the following formula (2) and the resulting nitrogen gas (N.sub.2) is extracted and determined quantitatively according to a thermal conductivity method. EQU 2N=N.sub.2 (g) (2)
In the above formulae, the element symbols underlined indicate that the underlined elements are occluded in molten titanium.
Titanium has a strong affinity for oxygen and nitrogen, so it is difficult to extract oxygen or nitrogen contained in titanium completely as carbon monoxide or nitrogen gas. Further, since titanium has a good wettability for a graphite crucible, it permeates into graphite upon melting with the result that only 1% or less of the actual content can be extracted.
In order to solve the above-mentioned problem, there has been proposed and practised a method (platinum bath method) in which platinum is melted together with a titanium sample. The platinum bath method is at present recommended and adopted widely because of superior analytical accuracy and reproducibility for the following reasons: (1) the solubility of oxygen or nitrogen in molten platinum is small and so the foregoing reaction is accelerated in extraction, (2) since the melting point of titanium and that of platinum is about the same (titanium: 1670.degree. C., platinum: 1773.degree. C.), the bath formation is easy, and (3) the solubility of carbon in molten platinum is also small and so the graphite crucible is not eroded. However, the platinum bath method is uneconomical because platinum is very expensive.